In the real life, AC Milan and Inter share the same stadium, the San Siro, called also Giuseppe Meazza. Since Giuseppe Meazza was an Inter legend and Inter and Milan are very rivals, when Inter plays at home, the stadium is called by everyone (commentators, etc.) Giuseppe Meazza stadium ("Welcome to the Giuseppe Meazza stadium"...) when instead Milan plays at home the stadium is called San Siro ("Welcome to the San Siro stadium") but exists only one stadium, the San Siro/Giuseppe Meazza. According to me, this situation has created confusion for FM programmers. Or Inter and Milan asked all videogame's developers to create two separate stadiums...
I don't know if I explained myself well, I don't speak English very well.